Centrifugal fan

ABSTRACT

A side wall of a centrifugal fan includes a gap expanding portion arranged to gradually expand a gap between an impeller and the side wall from an upstream end toward a downstream end with respect to a rotation direction of a rotating portion. In the centrifugal fan, an electronic component arranging portion of a board is arranged in an area surrounded by the gap expanding portion, the impeller, and an air outlet, and accordingly does not overlap with a motor or the impeller in an axial direction. The electronic component arranging portion is arranged in an area extending, in a circumferential direction about a central axis, from a position 180 degrees upstream from a middle of the air outlet downstream to the middle of the air outlet, that is, in an area where a wind channel has a large width.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal fan.

2. Description of the Related Art

Centrifugal fans used for internal cooling have often been installed inelectronic devices, such as personal computers. Once such a centrifugalfan is driven, an air current is produced inside a case of theelectronic device. This leads to a reduction in accumulation of heatinside the case. The structure of such a known centrifugal fan isdescribed, for example, in JP-A 2001-135964.

Centrifugal fans include circuit boards arranged to supply drivecurrents to windings. Also, in many known centrifugal fans, a magneticsensor arranged to detect the rotation rate of an impeller is mounted onthe circuit board. Thus, in many known centrifugal fans, a circuit boardhaving a variety of electronic components mounted thereon is disposed inthe vicinity of a rotating portion of a motor or the impeller.

However, when the electronic components on the circuit board arearranged to overlap with the motor or the impeller in an axialdirection, it is difficult to achieve a reduction in the axial dimensionof the centrifugal fan. In particular, recent years have seen anincreasing reduction in the thickness of notebook computers, tabletpersonal computers, and the like, and there has been an increasingdemand for centrifugal fans installed in such electronic devices todecrease in thickness.

One conceivable way of meeting the above demand is, for example, toarrange a portion of the circuit board on which the electroniccomponents are mounted in a wind channel on a radially outer side of theimpeller. However, when the circuit board, or a portion thereof, isarranged in the wind channel, wind impinges on the circuit board, andthis may cause an increase in wind noise of the centrifugal fan.

SUMMARY OF THE INVENTION

A centrifugal fan according to a preferred embodiment of the presentinvention includes a motor including a rotating portion, and arranged torotate the rotating portion about a central axis extending in a verticaldirection; an impeller arranged to rotate together with the rotatingportion; a board arranged to supply a drive current to the motor; and ahousing arranged to accommodate the rotating portion and the impeller,and including an upper air inlet and an air outlet. The housing includesa bottom plate arranged to spread substantially perpendicularly to thecentral axis on a lower side of the impeller; a top plate arranged tospread substantially perpendicularly to the central axis on an upperside of the impeller; and a side wall arranged to join an outer edgeportion of the bottom plate and an outer edge portion of the top plateto each other on a radially outer side of the impeller. The side wallincludes a gap expanding portion arranged to gradually expand a gapbetween the impeller and the side wall from an upstream end toward adownstream end with respect to a rotation direction of the rotatingportion. A circumferential extent of the gap expanding portion isarranged to be at least half a circumferential extent of the entire sidewall. The side wall includes a pair of edges arranged, respectively, ona downstream side and on an upstream side with respect to the rotationdirection. An opening between the pair of edges is the air outlet. Thetop plate includes the upper air inlet over the motor. The boardincludes an electronic component arranging portion arranged to have oneor more electronic components arranged thereon; a motor connectionportion arranged to extend from the electronic component arrangingportion toward the motor; and a draw-out portion arranged to extend fromthe electronic component arranging portion to an outside of the housing.The electronic component arranging portion is arranged in apredetermined area on the bottom plate. The predetermined area is anarea surrounded by the gap expanding portion, the impeller, and the airoutlet, and extending, in a circumferential direction about the centralaxis, from a position 180 degrees upstream from a middle of the airoutlet downstream to the middle of the air outlet.

According to the above preferred embodiment of the present invention,the electronic component arranging portion is arranged radially outwardof the impeller. Therefore, the electronic component arranging portiondoes not overlap with the motor or the impeller in an axial direction.This makes it possible to reduce the axial dimension of the centrifugalfan. In addition, the electronic component arranging portion is arrangedin an area where a wind channel has a large width. This contributes toreducing wind noise caused by the electronic component arrangingportion.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a horizontal cross-sectional view of a centrifugal fanaccording to a first preferred embodiment of the present invention.

FIG. 2 is a top view of a centrifugal fan according to a secondpreferred embodiment of the present invention.

FIG. 3 is a bottom view of the centrifugal fan according to the secondpreferred embodiment.

FIG. 4 is a horizontal cross-sectional view of the centrifugal fanaccording to the second preferred embodiment.

FIG. 5 is a vertical cross-sectional view of the centrifugal fanaccording to the second preferred embodiment.

FIG. 6 is a horizontal cross-sectional view of a centrifugal fanaccording to a modification of the second preferred embodiment.

FIG. 7 is a horizontal cross-sectional view of a centrifugal fanaccording to another modification of the second preferred embodiment.

FIG. 8 is a horizontal cross-sectional view of a centrifugal fanaccording to yet another modification of the second preferredembodiment.

FIG. 9 is a top view of a centrifugal fan according to yet anothermodification of the second preferred embodiment.

FIG. 10 is a horizontal cross-sectional view of a centrifugal fanaccording to yet another modification of the second preferredembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is assumedherein that a direction parallel to a central axis of a motor isreferred to by the term “axial direction”, “axial”, or “axially”, thatdirections perpendicular to the central axis of the motor are referredto by the term “radial direction”, “radial”, or “radially”, and that acircumferential direction about the central axis of the motor isreferred to by the term “circumferential direction”, “circumferential”,or “circumferentially”. It is also assumed herein that a verticaldirection is the axial direction, and that a side on which a top plateof a housing is arranged with respect to a bottom plate of the housingis defined as an upper side. The shape of each member or portion andrelative positions of different members or portions will be describedbased on the above assumptions. It should be noted, however, that theabove definitions of the vertical direction and the upper and lowersides are simply made for the sake of convenience in description, andshould not be construed to restrict in any way the orientation of acentrifugal fan according to any embodiment of the present inventionwhen in use.

1. First Preferred Embodiment

FIG. 1 is a horizontal cross-sectional view of a centrifugal fan 1Aaccording to a first preferred embodiment of the present invention. Asillustrated in FIG. 1, the centrifugal fan 1A includes a motor 10A, animpeller 20A, a housing 30A, and a board 40A.

The motor 10A includes a stationary portion fixed to the housing 30A,and a rotating portion 60A supported to be rotatable with respect to thestationary portion. The motor 10A is arranged to rotate the rotatingportion 60A about a central axis 9A extending in a vertical direction.The impeller 20A is arranged to rotate together with the rotatingportion 60A. The housing 30A is arranged to accommodate the rotatingportion 60A and the impeller 20A, and includes an upper air inlet 321Aand an air outlet 333A. The board 40A is arranged to supply drivecurrents to the motor 10A.

The housing 30A includes a bottom plate 31A, a top plate, and a sidewall 33A. The bottom plate 31A is arranged to spread substantiallyperpendicularly to the central axis 9A on a lower side of the impeller20A. The top plate is arranged to spread substantially perpendicularlyto the central axis 9A on an upper side of the impeller 20A. The sidewall 33A is arranged to join an outer edge portion of the bottom plate31A and an outer edge portion of the top plate to each other on aradially outer side of the impeller 20A. The side wall 33A includes agap expanding portion 334A arranged to gradually expand a gap betweenthe impeller 20A and the side wall 33A from an upstream end toward adownstream end with respect to a rotation direction of the rotatingportion 60A. The circumferential extent of the gap expanding portion334A is arranged to be at least half the circumferential extent of theentire side wall 33A.

The top plate includes the aforementioned upper air inlet 321A over themotor 10A, as indicated by a chain double-dashed line in FIG. 1. Theside wall 33A includes a pair of edges 331A and 332A arranged,respectively, on a downstream side and on an upstream side with respectto a rotation direction of the motor 10A. An opening between the pair ofedges 331A and 332A is the aforementioned air outlet 333A.

The board 40A includes an electronic component arranging portion 41A, amotor connection portion 42A, and a draw-out portion 43A. An electroniccomponent 411A is arranged on the electronic component arranging portion41A. The motor connection portion 42A is arranged to extend from theelectronic component arranging portion 41A toward the motor 10A. Thedraw-out portion 43A is arranged to extend from the electronic componentarranging portion 41A to an outside of the housing 30A.

The electronic component arranging portion 41A of the board 40A isarranged in an area 70A on the bottom plate 31A, the area 70A beingrepresented by a broken line in FIG. 1. The area 70A is surrounded bythe gap expanding portion 334A, the impeller 20A, and the air outlet333A. When the electronic component arranging portion 41A is arrangedradially outward of the impeller 20A as described above, the electroniccomponent arranging portion 41A does not overlap with the motor 10A orthe impeller 20A in the axial direction. This makes it possible toreduce the axial dimension of the centrifugal fan 1A.

The area 70A is an area which extends, in a circumferential directionabout the central axis 9A, from a position 180 degrees upstream from amiddle of the air outlet 333A downstream to the middle of the air outlet333A. The electronic component arranging portion 41A is thereforearranged in an area where a wind channel has a large width. Thiscontributes to reducing wind noise caused by the electronic componentarranging portion 41A.

2. Second Preferred Embodiment

Next, a second preferred embodiment of the present invention will now bedescribed below. FIG. 2 is a top view of a centrifugal fan 1 accordingto the second preferred embodiment. FIG. 3 is a bottom view of thecentrifugal fan 1. FIG. 4 is a horizontal cross-sectional view of thecentrifugal fan 1. FIG. 5 is a vertical cross-sectional view of thecentrifugal fan 1 taken along line A-A in FIGS. 2 to 4.

The centrifugal fan 1 is installed in an electronic device, such as anotebook computer, and is used to cool an inside of the electronicdevice. As illustrated in FIGS. 2 to 5, the centrifugal fan 1 accordingto the present preferred embodiment includes a motor 10, an impeller 20,a housing 30, and a board 40.

The motor 10 is arranged to rotate the impeller 20 in accordance withdrive currents. As illustrated in FIG. 5, the motor 10 includes astationary portion 50 fixed to the housing 30, and a rotating portion 60supported to be rotatable with respect to the stationary portion 50. Themotor 10 is arranged to rotate the rotating portion 60 about a centralaxis 9. The impeller 20 is arranged to rotate together with the rotatingportion 60. The stationary portion 50 includes a joining member 51, astator core 52, windings 53, a sleeve 54, and a cap 55. The rotatingportion 60 includes a shaft 61, a rotor holder 62, and a plurality ofmagnets 63.

The joining member 51 is fixed to a bottom plate 31 of the housing 30.Each of the stator core 52 and the sleeve 54 is supported by the joiningmember 51. The stator core 52 includes a plurality of teeth 521 arrangedto extend radially with respect to the central axis 9. Each of thewindings 53 is defined by a conducting wire wound around a separate oneof the teeth 521. The sleeve 54 is a substantially cylindrical memberfixed to an inner circumferential surface of the joining member 51. Thecap 55 is arranged to close a lower opening of the sleeve 54.

The shaft 61 is a columnar member arranged to extend in an axialdirection. The shaft 61 is inserted inside the sleeve 54. The rotorholder 62 includes an inner cylindrical portion 621, a plate portion622, and an outer cylindrical portion 623. The inner cylindrical portion621 is arranged to surround an outer circumferential surface of theshaft 61. In addition, the inner cylindrical portion 621 is arranged toextend downward from the plate portion 662. The plate portion 622 isarranged to extend radially outward from an upper end portion of theshaft 61. The outer cylindrical portion 623 is arranged to extenddownward from an outer edge portion of the plate portion 622. Themagnets 63 are fixed to an inner circumferential surface of the outercylindrical portion 623 on a radially outer side of the stator core 52.In addition, the magnets 63 are arranged in a circumferential directionsuch that north and south poles alternate with each other. Although theplurality of magnets 63 are arranged in the circumferential direction inthe present preferred embodiment, a ring-shaped magnet in which northand south poles are arranged alternately in the circumferentialdirection may be used in other preferred embodiments of the presentinvention.

A lubricating fluid 11 is arranged between a combination of the sleeve54 and the cap 55 of the stationary portion 50 and a combination of theinner cylindrical portion 621 and the shaft 61 of the rotating portion60. In the motor 10, the sleeve 54, the cap 55, the shaft 61, and theinner cylindrical portion 621 are arranged to together define a fluiddynamic bearing arranged to allow the stationary portion 50 and therotating portion 60 to rotate relative to each other through thelubricating fluid 11. A polyolester oil or a diester oil is used as thelubricating fluid 11, for example.

Once the drive currents are supplied to the windings 53 through theboard 40, magnetic flux is generated around each of the teeth 521 of thestator core 52. Then, a circumferential torque is produced byinteraction between the magnetic flux of the teeth 521 and that of themagnets 63, so that the rotating portion 60 is caused to rotate aboutthe central axis 9 with respect to the stationary portion 50.

The impeller 20 includes an annular impeller base portion 21 and aplurality of blades 22. The impeller base portion 21 is fixed to therotating portion 60. Specifically, the impeller base portion 21 is fixedto an outer circumferential surface of the outer cylindrical portion 623of the rotor holder 62. The blades 22 are arranged at regular intervalsin the circumferential direction as represented by chain double-dashedlines in FIG. 4. Each of the blades 22 is arranged to extend radiallyoutward from the impeller base portion 21. The impeller base portion 21and the blades 22 are defined as a single resin member by, for example,an injection molding process. Note, however, that the impeller baseportion 21 and the blades 22 may be defined by separate members. Theimpeller base portion 21 and the blades 22 are arranged to rotate aboutthe central axis 9 together with the rotating portion 60 of the motor10.

The housing 30 includes the bottom plate 31, a top plate 32, and a sidewall 33. The bottom plate 31 is arranged to spread substantiallyperpendicularly to the central axis 9 on a lower side of the impeller20. The top plate 32 is arranged to spread substantially perpendicularlyto the central axis 9 on an upper side of the impeller 20. The side wall33 is arranged to partially join an outer edge portion of the bottomplate 31 and an outer edge portion of the top plate 32 to each other ona radially outer side of the impeller 20. The impeller 20 and therotating portion 60 of the motor 10 are accommodated in an interiorspace of the housing 30, which is surrounded by the bottom plate 31, thetop plate 32, and the side wall 33.

As illustrated in FIGS. 2 and 5, the top plate 32 includes an upper airinlet 321 arranged to extend in the vertical direction therethrough. Theupper air inlet 321 is arranged over the motor 10. In addition, theupper air inlet 321 is arranged in the shape of a circle centered on thecentral axis 9 in a plan view. The side wall 33 includes a pair of edges331 and 332 arranged, respectively, on a downstream side and on anupstream side with respect to a rotation direction of the impeller 20.An opening as an air outlet 333 is defined between the pair of edges 331and 332.

Once the impeller 20 is rotated, a gas is drawn into the housing 30through the upper air inlet 321. The gas drawn into the housing 30receives a centrifugal force caused by the impeller 20, and is caused toflow in the circumferential direction in a wind channel 34 definedbetween the impeller 20 and the side wall 33, as indicated by an arrowin FIG. 4. The gas is then caused to travel from the wind channel 34 tothe air outlet 333, and be discharged out of the housing 30 through theair outlet 333.

As illustrated in FIG. 4, the radial width of the wind channel 34defined between the side wall 33 and the impeller 20 is arranged togradually increase from an upstream end toward a downstream end withrespect to a rotation direction of the rotating portion 60. In otherwords, the side wall 33 includes a gap expanding portion 334 arranged togradually expand a radial gap between the impeller 20 and the side wall33 from an upstream end toward a downstream end with respect to therotation direction. The circumferential extent of the gap expandingportion 334 is arranged to be at least half the circumferential extentof the entire side wall 33.

An electronic circuit configured to supply the drive currents to themotor 10 is mounted on the board 40. The board 40 according to thepresent preferred embodiment is a flexible printed circuit board. Theboard 40 includes an electronic component arranging portion 41, a motorconnection portion 42, and a draw-out portion 43. Each of the electroniccomponent arranging portion 41 and the motor connection portion 42 isfixed to an upper surface of the bottom plate 31 of the housing 30. Oneor more electronic components 411 are arranged on the electroniccomponent arranging portion 41. The electronic component arrangingportion 41 accordingly includes a portion that has an increased axialheight because of the electronic component(s) 411.

The motor connection portion 42 is arranged to extend from theelectronic component arranging portion 41 toward the motor 10. Four landportions 421 are each arranged in the vicinity of an end portion of themotor connection portion 42 on a side near the motor 10. In the presentpreferred embodiment, the four land portions 421 are used for a U phase,a V phase, a W phase, and common, respectively. End portions of thewindings 53 of the motor 10 are connected to the land portions 421through a solder.

The draw-out portion 43 is arranged to extend from the electroniccomponent arranging portion 41 to an outside of the housing 30. In thepresent preferred embodiment, the draw-out portion 43 is arranged tofirst extend radially inward from the electronic component arrangingportion 41, and then be drawn out of the housing 30 through a draw-outopening 311 defined in the bottom plate 31 of the housing 30. Thehousing 30 according to the present preferred embodiment includes thedraw-out opening 311 separately from the upper air inlet 321 and the airoutlet 333. A connector is arranged at a top end of the draw-out portion43. The connector is connected to a power supply unit.

The electronic component arranging portion 41 is arranged in the windchannel 34. Therefore, a wind blowing in the wind channel 34 can be usedto cool the electronic component(s) 411 on the electronic componentarranging portion 41. The board 40 according to the present preferredembodiment has mounted thereon a so-called sensorless drive circuit,which does not include a magnetic sensor arranged to detect the rotationrate of the rotating portion 60. It is therefore possible to arrange theelectronic component arranging portion 41 of the board 40 at a positionaway from the magnets 63 of the motor 10.

The electronic component arranging portion 41 is arranged in an areasurrounded by a radially outer end portion of the impeller 20, an innercircumferential surface of the gap expanding portion 334 of the sidewall 33, and the air outlet 333. That is, the electronic componentarranging portion 41 is arranged radially outward of the impeller 20.When the electronic component arranging portion 41 is arranged asdescribed above, the electronic component arranging portion 41 does notoverlap with the motor 10 or the impeller 20 in the axial direction.This makes it possible to reduce the axial dimension of the centrifugalfan 1.

In particular, the board 40 according to the present preferredembodiment is a flexible printed circuit board. The board 40 itselftherefore has a reduced axial dimension compared to a rigid board, suchas a glass epoxy board. This leads to an additional reduction in theaxial dimension of the centrifugal fan 1.

If the electronic component arranging portion were arranged in an areawhere the wind channel has a small width or in the vicinity of theimpeller, wind noise caused by the electronic component arrangingportion would be louder. In view of this consideration, the electroniccomponent arranging portion 41 is arranged in the vicinity of the edge331 of the side wall 33 on the downstream side with respect to therotation direction in the present preferred embodiment. Morespecifically, the electronic component arranging portion 41 is arrangednear and along both the side wall 33 and the air outlet 333. In thismanner, the electronic component arranging portion 41 is arranged faraway from the impeller 20. A reduction in the wind noise caused by theelectronic component arranging portion 41 is thereby achieved.

In order to reduce the wind noise caused by the electronic componentarranging portion 41, it is desirable that the electronic componentarranging portion 41 should be arranged in an area where the windchannel 34 has a large radial width. It is preferable, for example, thatthe electronic component arranging portion 41 should be arranged in anarea which extends, in the circumferential direction about the centralaxis 9, from a position 180 degrees upstream from a middle of the airoutlet 333 downstream to the middle of the air outlet 333. Moreover, afurther reduction in the wind noise caused by the electronic componentarranging portion 41 is achieved when the electronic component arrangingportion 41 is arranged in an area which extends, in the circumferentialdirection about the central axis 9, from a position 90 degrees upstreamfrom the middle of the air outlet 333 downstream to the middle of theair outlet 333.

Furthermore, in the present preferred embodiment, the electroniccomponent arranging portion 41 is arranged such that the distancebetween the electronic component arranging portion 41 and the side wall33 is smaller than the distance between the electronic componentarranging portion 41 and the impeller 20. The electronic componentarranging portion 41 can thus be arranged far away from the impeller 20.A further reduction in the wind noise caused by the electronic componentarranging portion 41 is thereby achieved.

As illustrated in FIG. 4, in the present preferred embodiment, thedraw-out opening 311 of the bottom plate 31 is arranged radially inwardof the radially outer end portion of the impeller 20 in a plan view. Thedraw-out opening 311 is thus arranged not to face the wind channel 34.This contributes to reducing the likelihood of a leakage of a gasflowing in the wind channel 34 through the draw-out opening 311. This inturn contributes to increasing static pressure of the centrifugal fan 1.Note that the draw-out opening 311 may be arranged radially inward of aradially outer edge portion of the impeller base portion 21 in a planview in order to achieve a further reduction in the likelihood of theleakage of the gas through the draw-out opening 311.

In the present preferred embodiment, at least one of the land portions421 is arranged in the area which extends, in the circumferentialdirection about the central axis 9, from the position 180 degreesupstream from the middle of the air outlet 333 downstream to the middleof the air outlet 333. This leads to a decreased wiring distance betweenthe electronic component(s) 411 on the electronic component arrangingportion 41 and the land portions 421 of the motor connection portion 42.The decreased wiring distance leads to reduced electrical noise betweenthe electronic component arranging portion 41 and the windings 53.

Moreover, in the present preferred embodiment, wires which connect theelectronic component(s) 411 and the land portions 421 to each other areeach arranged to extend without bending at an acute angle. The wiringdistance between the electronic component(s) 411 and the land portions421 is thereby further decreased. This leads to a further reduction inthe electrical noise between the electronic component arranging portion41 and the windings 53.

In particular, the board 40 according to the present preferredembodiment has the sensorless drive circuit mounted thereon. Thesensorless drive circuit controls the drive currents based on slightinduced voltages generated in the windings 53. Therefore, the electricalnoise tends to easily affect the control of drive of the motor 10.However, a layout of the board 40 according to the present preferredembodiment achieves a reduction in the electrical noise between theelectronic component arranging portion 41 and the windings 53 asdescribed above, which enables the sensorless drive circuit to performthe drive control with increased accuracy.

3. Example Modifications

While preferred embodiments of the present invention have been describedabove, it is to be understood that the present invention is not limitedto the above-described preferred embodiments.

The draw-out opening may be arranged radially outward of the radiallyouter end portion of the impeller in a plan view. This makes it possibleto decrease the distance between the electronic component arrangingportion and the draw-out opening as compared to the case of theabove-described second preferred embodiment. This makes it possible toreduce the length of the draw-out portion.

For example, as is the case with a centrifugal fan 1B according to amodification of the second preferred embodiment illustrated in FIG. 6, adraw-out opening 335B may be defined in a side wall 33B of a housing30B. In the case of FIG. 6, a draw-out portion 43B of a board 40B isarranged to directly extend radially outward from an electroniccomponent arranging portion 41B to the draw-out opening 335B withoutextending radially inward. As a result, the length of the draw-outportion 43B is shorter than that of the draw-out portion 43 according tothe second preferred embodiment. A shorter length of the draw-outportion 43B leads to a reduction in electrical noise introduced betweenthe power supply unit and the electronic component arranging portion41B.

FIG. 7 is a horizontal cross-sectional view of a centrifugal fan 1Caccording to another modification of the second preferred embodiment. Inthe case of FIG. 7, a bottom plate 31C of a housing 30C includes aplurality of lower air inlets 312C. Each lower air inlet 312C is athrough hole arranged under a rotating portion 60C of a motor or underan impeller 20C. In this case, a gas can be introduced into the housing30C through both an upper air inlet and the lower air inlets 312C.

Moreover, in the case of FIG. 7, a draw-out portion 43C of a board 40Cis arranged to be drawn out of the housing 30C through one of the lowerair inlets 312C. When the lower air inlets 312C are used to draw out thedraw-out portion 43C, it is not necessary to provide an openingdedicated to the draw-out portion 43C.

FIG. 8 is a horizontal cross-sectional view of a centrifugal fan 1Daccording to yet another modification of the second preferredembodiment. In the case of FIG. 8, a draw-out opening 335D is arrangedat a position on an opposite side of a motor with respect to anelectronic component arranging portion 41D. In addition, a bottom plate31D of a housing 30D includes a plurality of lower air inlets 312D. Eachlower air inlet 312D is a through hole arranged under a rotating portion60D of the motor or under an impeller 20D.

Moreover, in the case of FIG. 8, a draw-out portion 43D of a board 40Dis arranged to extend to the draw-out opening 335D along ribs 313D eacharranged between adjacent ones of the lower air inlets 312D. This allowsthe draw-out portion 43D to extend from the electronic componentarranging portion 41D to the draw-out opening 335D without preventinggas introduction through the lower air inlets 312D.

FIG. 9 is a top view of a centrifugal fan 1E according to yet anothermodification of the second preferred embodiment. In the case of FIG. 9,a draw-out portion 43E of a board 40E is arranged to be drawn out of ahousing 30E through an air outlet 333E. After being drawn out throughthe air outlet 333E, the draw-out portion 43E is bent upward to extendabove an upper surface of a top plate 32E and extend sideways. When theair outlet 333E is used to draw out the draw-out portion 43E asdescribed above, the housing 30E does not need to include an openingdedicated to the draw-out portion. Therefore, both a reduction inrigidity of the housing 30E and the likelihood of a leakage of the gasout of the housing 30E can be reduced. Note that, after being drawn outthrough the air outlet 333E, the draw-out portion 43E may be bentdownward to extend below a lower surface of a bottom plate and extendsideways.

FIG. 10 is a horizontal cross-sectional view of a centrifugal fan 1Faccording to yet another modification of the second preferredembodiment. In the case of FIG. 10, an upper surface of an electroniccomponent arranging portion 41F of a board 40F is covered with a pottingportion 44F made of a resin. In this case, electronic components 411F onthe electronic component arranging portion 41F are protected from an aircurrent while the electronic component arranging portion 41F is arrangedin a wind channel 34F.

Centrifugal fans according to other preferred embodiments of the presentinvention may differ in details of structure from the centrifugal fansaccording to the above-described preferred embodiments and themodifications thereof. For example, the number of land portions arrangedin the motor connection portion of the board may be one, two, three, ormore than four. Also, the side wall and one of the bottom plate and thetop plate of the housing may be defined by a single member.

Also, the board may be a rigid board, such as a glass epoxy board. Inthe case where the rigid board is used, the draw-out portion may be aconducting wire. Also, a fluid dynamic bearing mechanism may be used asa bearing portion of the motor as in the above-described secondpreferred embodiment, or alternatively, a bearing mechanism of anothertype, such as a plain bearing, may be used.

Also, centrifugal fans according to other preferred embodiments of thepresent invention may be installed in devices other than electronicdevices. Also, centrifugal fans according to other preferred embodimentsof the present invention may be used for purposes other than cooling.Note, however, that the present invention is particularly useful forcentrifugal fans used in notebook PCs or tablet PCs, since a reductionin thickness is particularly demanded of the notebook PCs and the tabletPCs.

Also note that features of the above-described preferred embodiments andthe modifications thereof may be combined appropriately as long as noconflict arises.

The present invention is applicable to centrifugal fans.

What is claimed is:
 1. A centrifugal fan comprising: a motor including arotating portion, and arranged to rotate the rotating portion about acentral axis extending in a vertical direction; an impeller arranged torotate together with the rotating portion; a board arranged to supply adrive current to the motor; and a housing arranged to accommodate therotating portion and the impeller, and including an upper air inlet andan air outlet; wherein the housing includes: a bottom plate arranged tospread substantially perpendicularly to the central axis on a lower sideof the impeller; a top plate arranged to spread substantiallyperpendicularly to the central axis on an upper side of the impeller;and a side wall arranged to join an outer edge portion of the bottomplate and an outer edge portion of the top plate to each other on aradially outer side of the impeller; the side wall includes a gapexpanding portion arranged to gradually expand a gap between theimpeller and the side wall from an upstream end toward a downstream endwith respect to a rotation direction of the rotating portion; acircumferential extent of the gap expanding portion is arranged to be atleast half a circumferential extent of the entire side wall; the sidewall includes a pair of edges arranged, respectively, on a downstreamside and on an upstream side with respect to the rotation direction; anopening between the pair of edges is the air outlet; the top plateincludes the upper air inlet over the motor; the board includes: anelectronic component arranging portion arranged to have one or moreelectronic components arranged thereon; a motor connection portionarranged to extend from the electronic component arranging portiontoward the motor; and a draw-out portion arranged to extend from theelectronic component arranging portion to an outside of the housing; theelectronic component arranging portion is arranged in a predeterminedarea on the bottom plate; and the predetermined area is an areasurrounded by the gap expanding portion, the impeller, and the airoutlet, and extending, in a circumferential direction about the centralaxis, from a position 180 degrees upstream from a middle of the airoutlet downstream to the middle of the air outlet.
 2. The centrifugalfan according to claim 1, wherein the board is a flexible printedcircuit board.
 3. The centrifugal fan according to claim 1, wherein adistance between the electronic component arranging portion and the sidewall is arranged to be smaller than a distance between the electroniccomponent arranging portion and the impeller.
 4. The centrifugal fanaccording to claim 2, wherein a distance between the electroniccomponent arranging portion and the side wall is arranged to be smallerthan a distance between the electronic component arranging portion andthe impeller.
 5. The centrifugal fan according to claim 3, wherein theelectronic component arranging portion is arranged in a vicinity of theedge of the side wall on the downstream side with respect to therotation direction.
 6. The centrifugal fan according to claim 4, whereinthe electronic component arranging portion is arranged in a vicinity ofthe edge of the side wall on the downstream side with respect to therotation direction.
 7. The centrifugal fan according to claim 1, whereinthe housing includes, separately from the upper air inlet and the airoutlet, a draw-out opening through which the draw-out portion isarranged to be drawn out of the housing.
 8. The centrifugal fanaccording to claim 7, wherein the draw-out opening is arranged radiallyinward of a radially outer end portion of the impeller in a plan view.9. The centrifugal fan according to claim 7, wherein the draw-outopening is arranged radially outward of a radially outer end portion ofthe impeller in a plan view.
 10. The centrifugal fan according to claim9, wherein the draw-out opening is defined in the side wall.
 11. Thecentrifugal fan according to claim 7, wherein the impeller includes anannular impeller base portion fixed to the rotating portion, and aplurality of blades arranged to extend radially outward from theimpeller base portion; and the draw-out opening is arranged radiallyinward of a radially outer edge portion of the impeller base portion ina plan view.
 12. The centrifugal fan according to claim 1, wherein theelectronic component arranging portion is arranged in an area extending,in the circumferential direction about the central axis, from a position90 degrees upstream from the middle of the air outlet downstream to themiddle of the air outlet.
 13. The centrifugal fan according to claim 1,wherein the bottom plate includes a lower air inlet arranged under themotor or the impeller; and the draw-out portion is arranged to be drawnout of the housing through the lower air inlet.
 14. The centrifugal fanaccording to claim 1, wherein the bottom plate includes a plurality oflower air inlets each of which is arranged under the motor or theimpeller, and a rib arranged between adjacent ones of the lower airinlets; and the draw-out portion is arranged to extend along the rib.15. The centrifugal fan according to claim 1, wherein the draw-outportion is arranged to be drawn out of the housing through the airoutlet.
 16. The centrifugal fan according to claim 1, wherein the motorconnection portion includes land portions to which windings of the motorare connected; and at least one of the land portions is arranged in anarea extending, in the circumferential direction about the central axis,from the position 180 degrees upstream from the middle of the air outletdownstream to the middle of the air outlet.
 17. The centrifugal fanaccording to claim 16, wherein wires connecting the one or moreelectronic components on the electronic component arranging portion andthe land portions to each other are each arranged to extend withoutbending at an acute angle.
 18. The centrifugal fan according to claim 1,further comprising a potting portion made of a resin, and arranged tocover the electronic component arranging portion.